A type of friction stir welding tool having a rotary shoulder rotated integrally with a probe and a type of friction stir welding tool having a rotary probe and a stationary shoulder that is not rotated are known as friction stir welding tools (tools for friction stir welding) used in a friction stir welding device.
As the friction stir welding tool having the stationary shoulder, a type of friction stir welding tool in which the stationary shoulder has a face that comes into contact with both workpiece surfaces forming corners for the purpose of performing friction stir welding on corners (inner corners) of the workpieces to be welded is known.
Further, a device for performing friction stir welding on two corners, which are formed by abutting a horizontal workpiece (a horizontal member) and a workpiece (an erected member) erected on the horizontal workpiece from opposite sides of the erected workpiece using a pair of friction stir welding tools (for example, see Patent Document 1) has been conventionally proposed as the friction stir welding device using the above-mentioned friction stir welding tool for welding the corners.
This friction stir welding device includes a pressing mechanism for applying a pressing load to each of the friction stir welding tools. This pressing mechanism is configured to have an upward/downward moving means and a leftward/rightward moving means. In addition, the pressing mechanism controls outputs of both the upward/downward moving means and the leftward/rightward moving means in order to equalize directions of both a vector direction of the pressing load applied to the friction stir welding tool and a direction of the central axis of a probe, which is a stir shaft.
Further, when friction stir welding of the corners is performed by the friction stir welding tool having the stationary shoulder, a method called AdStir configured to form R (a fillet caused by buildup) at the welded corners by adding a welding filler has also been conventionally proposed (for example, see Non-Patent Document 1).
Meanwhile, in the friction stir welding using a type of friction stir welding tool having the rotary shoulder, frictional heat can be generated at a place at which the rotary shoulder is in contact with the workpiece.
In contrast, in the friction stir welding using a type of friction stir welding tool having the stationary shoulder, since no frictional heat occurs at a place at which the stationary shoulder is in contact with the workpiece, the frictional heat needs to be generated at the workpiece only by the rotary probe.
For this reason, when the type of friction stir welding tool having the stationary shoulder is used, it is important to control a pressing load (a pressing force) applied to the friction stir welding tool.